Telephones are among the most common instruments in the telecommunications field. As such, telephones are utilized extensively throughout the various segments of the economy (e.g., business, industrial, and governmental organizations, to name a few). In a typical organization, telephones are used to receive calls from a variety of call "originators". These calls can be from people inside the organization or people outside the organization. The calls can be intercom based (e.g., within a specific building or campus setting), or externally originated telephone calls (e.g., utilizing the telephone company network). Due to the wide variety of possible originators, it has become common to include systems within the telephone which provide information regarding an incoming phone call. The information can include the origin of the call or the identity of the caller, among other things. It is beneficial to the user to have such information prior to actually "answering" the phone call.
One obvious method of obtaining the origin and identity of a phone call is the use of a receptionist or executive assistant to "answer" the call prior to the intended recipient of the call answering it. A more modern and efficient method is the use of specialized devices within the telephone receiver to indicate the origin and identity of the phone call. For example, some modern telephone receivers include built in alphanumeric displays to show information regarding a phone call before the call is answered. These telephone receivers include the necessary circuitry for implementing and supporting the included alphanumeric display. This solution is typically too costly and too complex for most applications. A much more commonly implemented solution is to vary the tone or other such characteristic of the audible "ring" of the telephone. Circuitry implementing a variable ringer is included within the telephone. Consequently, various types of incoming calls (e.g., an intercom based call, a long distance call, and the like) each have a distinctive audible ring characteristic.
There is a problem, however, in that the circuitry implementing the variable ringer significantly increases the cost of the overall telephone. Although a variable ringer implementation may be less expensive than the incorporation an alphanumeric display, the circuitry implementing the variable ringer adds a significant additional amount of expense to the cost of manufacturing the telephone. Most prior art variable ringers include a specialized variable ringer interface circuit. The prior art ringer interface circuits incorporate specialized analog circuitry for implementing the variable, distinctive ring characteristic. Such specialized analog circuitry typically includes sine wave oscillators for generating the various distinctive ring signals. Sine wave oscillators are disadvantageous because the oscillators require special filtering. The signal generated by the oscillators needs to be filtered prior to amplification, increasing total component count. Sine wave oscillators also consume excessive amounts of power, limiting their usefulness in power limited applications (e.g., portable phones, cellular phones, and the like). Additionally, the analog circuitry comprising the sine wave oscillators are more susceptible to noise than other digital circuitry included in the telephone.
Thus, what is required is a system which overcomes the problems associated with prior art variable ringer implementations. The required system should be less expensive than prior art sine wave oscillator based variable ringers. The required system should not consume excessive amounts of power. In addition, the required system should be relatively insensitive to noise. The present invention provides a novel solution to the above requirements.